Dandruff doesn't occur on genital areas. You may be suffering from tinea cruris which is fungal infection of the inner thighs and buttocks area. It can be treated by taking four to six weeks of anti fungal treatment which includes tablets along with creams. Do not use soap over that area. Mistreatment with over the counter Steroid containing creams like fourderm, panderm, quadriderm, hh zole, candid b etc lead to repeated case of recurrence and also side effects due to application. Do not use steroid containing combination creams. Please call me or contact me using online consult option with photos for detailed prescription.